A print-head-voltage controlling device is conventionally known that steps down a source voltage outputted from a switching power supply unit with a print-head-voltage control circuit to obtain driving voltages of a plurality of print heads. With this technology, an inexpensive three-terminal regulator is used as the print-head-voltage control circuit. In order to obtain stable outputs, a voltage difference between an IN terminal and an OUT terminal of the three-terminal regulator is set to a fixed voltage (for example, 1.5V) or higher.